This invention relates generally to a duplicating machine and, more particularly, to a machine for duplicating images on both sides of copy sheets, hereinafter sometimes referred to as "duplexing".
Duplicating machines are available for the production of copies with images formed on one side of the copy sheets. Such equipment can be reliably operated at highly satisfactory production rates. Because of the advantages of duplexing in savings of the amount of paper employed, savings in the space occupied by the copies produced, and savings in production time and equipment costs, it is desirable to provide apparatus for imaging both sides of a copy sheet.
Duplexing often is effected by duplicating machines employing a single printing couple to thereby provide a compact unit that may be utilized in small work areas and conserve the amount of floor space required in which to operate the equipment. However, single printing couples for duplex printing require relatively large and expensive master cylinders, blanket cylinders and impression cylinders because of the multiple images required on a single cylinder. Sometimes the cost is prohibitive. In addition, relatively complex gripper mechanisms are required on the impression cylinder, as well as complex mechanisms for handling sheets released from the impression cylinder and re-feeding the sheets back to the gripper mechanisms on the cylinder.
Consequently, it often is desirable to utilize plural printing couples employing less expensive cylinders and gripper mechanisms where the work area or floor space in which the mechanism is to be utilized is not a premium. There have been various approaches in the printing and duplicating field for printing a copy sheet on a first side by a first printing couple and then on the opposite side by a second printing couple.
One approach to such duplex printing has been to provide a sheet handling mechanism for passing a copy sheet through a first printing couple for imaging one side of the sheet in a first direction and advancing the sheet in a second, substantially perpendicular direction to a second printing couple. As the sheet changes direction, it is inverted by a turn-over device and simultaneously directed to the second printing couple for imaging the opposite side of the sheet. Such machines have an L-shaped configuration of the sheet advancing path and are considerably more expensive and complex than simple straight-line, tandemly arranged printing apparatus.
Therefore, the most prominent approach in the printing and duplicating field has been to print a copy sheet on a first side by a first printing couple and then on the opposite side by a second, tandemly arranged printing couple. Such tandemly arranged machines still have considerable problems in alignment, timing and other sheet parameters because the sheet most often is grasped at a lead edge when issuing from the first printing couple and then fed to the second printing couple whereat the opposite or trail edge of the sheet must be grasped in precise alignment and under strict timing conditions.
This invention is directed to solving such sheet handling problems, primarily in printing or duplicating machine arrangements utilizing tandemly arranged printing couples.